McConnell signaled in a floor speech that he might oppose Perez, calling him “a committed ideologue who appears willing, quite frankly, to say or do anything to achieve his ideological ends.”

In an interview with CQ Roll Call, Rubio was more direct, saying he plans to vote against Perez, the assistant attorney general in charge of the Justice Department’s Civil Rights Division whom President Barack Obama nominated for the Labor post on March 18.

“I’m not going to support his nomination,” the Florida Republican said. “I have tremendous admiration for his personal story and his qualifications. Unfortunately, I think his views are wrong and I think particularly, if you look at some of the left-wing activism that he’s been involved in and how he’s brought that into the Justice Department, to see that in the Labor Department I don’t think would be good for Americans.”

Rubio’s opposition could provide cover for other Republicans to oppose the nominee as well. Perez — whose family immigrated to the United States from the Dominican Republic — would, if confirmed, be the only Hispanic member of Obama’s second-term Cabinet, and the nomination battle comes as Rubio and some other Republicans have been trying to improve their party’s outreach to Hispanics because of their poor showing among that demographic group in last year’s elections.

Minority Whip John Cornyn, R-Texas, also expressed opposition Wednesday to Perez. Cornyn took to the floor to raise a number of issues that have become ammunition for Republicans in the confirmation fight.

At the top of that list is a charge that Perez, while at the DOJ, improperly brokered a deal with the city of St. Paul, Minn., in which the city withdrew from a Supreme Court lending discrimination case in exchange for the federal government agreeing not to join a pair of housing-related False Claims Act lawsuits against the city that were instigated by a whistle-blower.

Republicans have also seized on a 258-page internal report released by DOJ Inspector General Michael E. Horowitz in March cataloguing widespread mistrust and “deep ideological polarization” in the Voting Rights Section of the Civil Rights Division, a trend that dated back to the George W. Bush administration but that continued in the Obama era under Perez.